Maintworld 1/2017

CONDITION MONITORING
Process valve tagged for shipment to
Emerson IVS repair facility.
ing the traditional coating that can
degrade over time
• A live-loaded packing system
replaces the original manually
adjustable configuration to ensure
the integrity of the packing seal for
extended operating periods
Recently, Moog introduced a new Gas
Control Valve Assembly 64 K Upgrade
for General Electric 7FA turbines. It was
the first offering able to extend the maintenance
interval of gas control equipment
from the typical 48,000 hours of
operation to 64,000 hours.
To complete the 64 K Upgrade package,
the actuator and process valve are
returned to “zero-hour” condition. The
actuator receives a factory overhaul, and
the process valve undergoes a Fisher
Encore repair performed at an Emerson
IVS repair facility. The integrated
assembly overhaul is a 100 percent
OEM repair. This process ensures the
turbine’s valves are returned to as-new
specifications and performance, resetting
the inspection clock to hour zero.
For turbine plants with the Advanced
Gas Path Technology, the benefits of
synchronizing major inspection periods
means managers will never find themselves
trying to overhaul gas valves when
they have a much smaller outage window.
Of course, many operators see the
benefits of the extended life even if they
have the 48,000 maintenance interval
due to high confidence in the reliability
of the assembly.
Exchange programmes help
leverage planned outage
Risks during a scheduled outage are
eliminated through the so-called Advanced
Exchange Programme, which
offers a turbine owner rebuilt gas control
valves that arrive prior to the start
date of an outage. This allows managers
to remove the used valves and install
the rebuilt valves in sequence, saving
money and time. When considering the
complexity of an outage and all of the
tasks a maintenance manager must juggle,
having a spare actuator assembly on
hand when needed can help prevent the
cost of an extended outage or unplanned
downtime.
One example of a power plant that
effectively used its outage is a combined
cycle power plant in the Southeastern
U.S. that began planning for an extended
outage months in advance.
The plant’s managers had 21 days
for the inspection of each combustion
turbine and 18 days per steam turbine.
Managers had to refurbish fuel gas and
steam control valve assemblies during
these outages. To maintain reliability,
the plant had to return the equipment to
as-new condition. The plant managers
wanted OEM repairs and upgrades, and
the timeframe to perform the repairs
within the inspection window left no
margin for error. If power was offline
even for a single day, everyone knew the
lost revenue would be significant. Moog
service technicians proposed a service
plan that included a combination of
spares, repairs and exchange units to
meet the plant’s inspection schedules.
For the combustion turbine units,
the plant purchased one spare set of
actuators. These served dual roles as a
rotatable set during planned outages and
emergency spares during forced outages.
Technicians used the power plant’s
spares and a set of Moog’s exchange
units complete with process valves. At
the end of the preventative maintenance
outage, technicians returned the plant’s
spare set to the site and replaced the
Moog set in the exchange pool inventory.
The plant managers and service
technicians determined that the steam
turbines’ actuators and valves could be
repaired within the allotted time, too.
The plant’s managers coordinated the
repair and removed the steam process
valves from the actuators and sent the
actuators to Moog for repair. After completing
the actuator repairs, technicians
conducted a final acceptance test and
sent the actuators to the power station
with a two-year warranty. The plant
reassembled the valve to the actuator,
installed the assembly, and tested it for
commissioning.
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